(1) Field of the Invention
This invention relates to a process for producing phenols which are useful as a raw material for a phenol resin, a bisphenol resin, alkyl phenols and aniline and other compounds.
(2) Description of the Related Art
Phenol is the most typical example of phenols having a hydroxyl group in the aromatic ring, and the most typical process for producing phenol is a cumene process. The cumene process has problems in that it comprises many steps such as alkylation, oxidation and decomposition, and acetone is produced undesirably in an amount equimolar to phenol.
As other processes for the production of phenol, there are a Raschig process wherein benzene is chlorinated to chlorobenzene which is converted to phenol, and a toluene-oxidizing process wherein toluene is oxidized to benzoic acid which is converted to phenol. These processes have problems in that the apparatus is liable to corrode, an equipment cost is high because the processes comprise many production steps, and the processes are troublesome because handling of a solid and a slurry is needed.
With regard to polycyclic aromatic compounds having a hydroxyl group in the aromatic ring, a process is industrially established wherein a non-condensed ring compound such as diphenyl or a condensed ring compound such as naphthalene is sulfonated and the sulfonated product is converted to phenylphenol or naphthol, respectively. This process also has a problem such that the apparatus is liable to corrode due to an alkali or an acid.
To solve the problems arising in the above-mentioned processes for producing aromatic compounds having a hydroxyl group, a process has been proposed wherein a corresponding aromatic compound is directly oxidized to an intended phenol. For example, a process for producing phenol which is the most typical example of phenols has been proposed wherein benzene is oxidized at a high temperature of approximately 600.degree. C. or under mild conditions including about room temperature. More specifically, a process has been proposed in Japanese Unexamined Patent Publication No. 56-87527 in which benzene is directly oxidized to phenol in the presence of a catalyst comprising, for example, phosphorus oxide, zinc oxide and silver oxide, or phosphorus oxide, titanium oxide and siver oxide, and in the co-presence of methanol. Further, a process has been proposed in Japanese Unexamined Patent Publication No. 61-85338 in which benzene is reacted with oxygen to produce phenol in the presence of a metal porphyrin, imidazole, platinum and hydrogen.
In the conventional processes for directly oxidizing an aromatic compound to produce a phenol, the conversion of the aromatic compound and the selectivity to the phenol are not highly satisfactory.